Method of forming engraved markings in a ferrous article



Patented Feb. 4, 1947 METHOD OF FORMING ENGRAVED MARK- INGS IN A FERROUSARTICLE.

Clifford W. Mell, Moorestown, N. .l., assignor to Radio Corporation ofAmerica, a corporation of Delaware No Drawing. Application August 25,1944, Serial No. 551,271

4 Claims. 1

This invention relates to a method of engraving, and more particularlyto a method of forming engraved markings in ferrous articles having anorganic finishing coat thereon.

There are many types of equipments employing panels provided withvarious types of markings, such as lettering, numerals, or the like. Inmany of these equipments it has been found desirable to apply a suitableorganic finishing coat over the panels for the sake of protecting thepanels from the elements, for ornamental purposes, etc. In manyinstances, as in the case of electrical test equipment, panels of thetype under consideration have been made of aluminum or other lightmetal. Due to the scarcity of aluminum and other light metalsnecessitated by present conditions, panels of steel have been resortedto. The steel panels, like those of aluminum, are also desirablyfinished with an organic wrinkle finish on the front, and frequentlyalso with an enamel finish on the back, some panels havingportionscovered only by electroplated metal for the purpose of makingelectrical connection thereto.

Whatever the type of panel employed, it is desirable to apply letteringon the front thereof which must be en raved through the wrinkle finishinto the metal for the sake of permanence. Aluminum does not require anyprotective plating on the lettering, but steel panels must have thelettering protected against rust. It has been proposed, heretofore, tofinish the lettering engraved in steel by filling with white wax or thelike, but this has not been found satisfactory. Silver plating producesa finish which is more durable and also more satisfactory in appearance.However, due to the character of the organic finish, the silver cannotbe deposited by electroplating for more than a few minutes, since moreprolonged electroplating loosens the organic finishing coat and causesit to come oif. For this reason, it has been proposed to apply thesilver by immersion deposit in a humid atmosphere, but such deposits ofsilver, while not being detrimental to the organic finish, will preventrusting of the steel for only a few hours.

The primary object of my present invention is to provide an improvedmethod of engraving markings in steel panels or other ferrous articlesprovided with an organic finish, which method will not be subject to thedefects and limitations of prior art methods proposed for this purpose.

More particularly, it is an object of my present invention to provide animproved method of providing markings in ferrous articles having anorganic finishing coat thereon, together with a method of protectingboth the organic finish and the ferrous article so that neither will beinjured.

Another object of my present invention is to provide an improved methodof engraving markings in ferrous articles as aforesaid which Will resultin markings which stand out prominently and which are of lastingcharacter.

Still another object of my present invention is to provide an improvedmethod of engraving markings in steel panels. or the like covered with asuitable organic finish, together with a protective coat therefor, whichmethod will result in markings and a protective coat which willsuccessfully withstand a salt spray test at least hours, this being aprerequisite in many equipments employed in naval vessels.

It is also an object of my present invention to provide an improvedmethod of forming engraved markings and a protective coat therefor asaforesaid which are relatively inexpensive and highly efiicient.

In accordance with my present invention, the steel panel or the like inwhich the markings are to be formed is cleaned and treated with aphosphate to obtain a frosty, uniform, black coating of iron phosphate.A wrinkle or other suitable finish of organic material capable ofbecoming cured in the course of time is then carefully applied to theiron phosphate coating. The wrinkle or similar finish is then cureduntil a firm, hard finishing coat is obtained, but care should be takenthat this coat will not have been cured to the point of becomingbrittle. With most organic finishes, a curing time of from about 3 to 30days is sufiicient. The lettering or other marking is then engraved inthe finishing coat and the steel panel by cutting with an appropriate,sharp cutting tool, the tool preferably being one which forms the bottomof the letters fiat. After smoothing the engraved markings, they arecleaned by brushing gently with a soft brush and by treating With asolution of sodium cyanide. The engraved markings are then plated with asuitable adherent metal, such a cadmium or the like, after which thepanel is washed and plated with silver. When dry, the panel is thengiven a transparent, protective coating of clear lacquer. The engravingsformed and finished as above described Will be very durable, the organicfinish will not come loose during plating, and the finished panel can besubjected to a salt spray test of at least 100 hours at 35 C. Withoutfailure of either the wrinkle finish or the electroplating.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionitself, however, together with additional objects and advantagesthereof, will best be understood from the following more detaileddescription of one way of carrying it into practice:

Let it be assumed that the article to be treated is a steel panel whichis to be engraved with certain lettering or other desired markings. Thepanel is first thoroughly degreased in a suitable solvent or in vapor,or both, in known manner, after which it is alkaline cleaned asthoroughly as for electroplating, so that no water breaks appear afterdipping in 30 percent muriatic acid. The panel is then washed in clean,cold tap water, after which it is dipped in 30 to 50 percent muriaticacid and again thoroughly washed in clean, cold tap water. The panel isthen treated with phosphoric acid in a phosphate treating bath toprovide a thin, uniform, greyish-black, frosty, crystalline, surfacecoating of iron phosphate. This procedure is well known in the art andneed not be described in further detail, it being pointed out merelythat the iron phosphate provides a strong bond between the organicfinishing coat and the steel base so that the finishing coat will standup against the subsequent plating operations. The treated panel is thenagain washed thoroughly and dljed, after which masking tape may beplaced on all areas or portions thereof which are to receive plating ofappropriate metals to provide suitable electrical contacts for externalconnection where this is necessary.

The panel is then sprayed with a suitable grade of organic material in amanner to provide the type of finish desired, that is, smooth, wrinkled,orange peel, or the like. This finish may be applied either to bothsides of the panel, or only to the front thereof, and in the lattercase, the back of the panel may be coated with an appropriate grade ofenamel or the like. It is important that the organic finish be appliedcarefully and thoroughly, and care must be taken to completely coveralledges. The organic finish on the coated panel may then be baked inthe heat cycle to which'it is best adapted. With certain, conventional,organic materials used for wrinkle finishes, a baking time of the orderof 23 minutes at about 250 F. is satisfactory, but other baking cycles'may be found more desirable, depending upon the type of material usedand the thickness of coating desired; In any case, the baked finishshould be hard and firm but not brittle. 'It will usually be found thatthis condition is obtained with most conventional organic finishes in aperiod from about 3 days to about 30 days.- The particular materialwhich may be employed for the organic finish is not a part of thepresent invention, and any suitable material may be used.

After the finish has cured properly, the lettering orother markings areengraved with a sharp, preferably flat-bottomed, tool, since dullcutting tools tend to tear and loosen the organic finish. The cutting orengraving is performed in three distinct steps. The first cut should hejust through the organic finish; the second out should penetrate themetal of the steel panel to the proper depth; and the third cut is madeto smooth the surfaces of the markings in the organic finish and. in thepanel and to remove projections and burs in the engravings. The heavyelectroplate required to withstand severe corrotrical contact points forhooks or the like.

sion conditions will build up and emphasize every irregularity in theengraved letters; hence, it is imperative that the engraved surfaces beas smooth as possible in order to obtain plated letters which have agood appearance.

The engraved panel should thenbe protected from air until it is plated.This may be done by carefully wrapping in paper or other suitablewrapping. Electroplating should be performed within about 8 hours afterengraving or sufficient oxide will very likely form on the steel tointerfere with proper electroplating. At this point, the masking tape isremoved from the areas of the panels where electroplating is desired,and the engraved surfaces are cleaned and prepared for plating by gentlybrushing with a soft brush and a solution of cold sodium cyanidecontaining about 6 ounces of sodium cyanide per gallon. Conventionalmethods of preparing metal or plating are not suitable in this casebecause of the chances of injuring'the organic finish. Dummy racks orplates are then placed in a cadmium plating bath as cathodes and thecurrent density is adjusted so that the cathodes will plate at a ratejust below the gassing point. Enough of the organic finish on the top oron the back edge of the panel is carefully removed, as by cutting awaywith a knife, to provide elec- The panel is then placed in the cadmiumplating bath as a cathode and the current density is adjusted to allowfor any exposed areas, usually on the back of the panel, which are to beplated. The area of the engraved letters is usually too small to bedetermined and to be taken into account in the adjustment of the currentdensity, and therefore the, proper current density is adjusted to thedummy cathodes. Care must be taken that the engraved letters will notgas during plating, sin e gassing tends to lift and loosen the plating.Any other plating which does not gas during the plating operation andwhich, like the cadmium, will form an adherent metal coating, may bedeposited in place of the cadmium. When a flash of copper, for example,is deposited from a cyanide bath at a very low current density, it'maybe followed by acid copper or nickel.

Where the metal being plated is cadmium, the

plating should continue for about 15 minutes to obtain a deposit of fromabout 0.00025 inch to 0.0003 inch in thickness. Equivalent thicknessesof other metals would be satisfactory. When the plating operation hasbeen completed, the coated and plated panel is washed thoroughly incold, clean tap water. A silver strike is then applied for about 30seconds, and the panel is then placed in a silver plating bath for about10 minutes with a current density adjusted to about 5 amperes per squarefoot as measured .on cathodes having a square foot or more which may beplated along with the panel. This forms an electro-deposited coating ofsilver over the silver strike. The panel is then washed in a silverreclaim rinse, after which it is washed in clean, cold tap water. Thepanel should not be washed with hot water, as this may be detrimental.Excess liquid'is carefully blown off with an air jet which is notpermitted to come closer than 12 inches from the plated areas or injurymay result to the edges of the organic finish.

The panel is then dried for about 10 to 15 minutes, preferably in an aircirculating .oven operating at about F. to 200 F., and it'is thenpermitted to cool to room temperature.

Within a period of time sufiicient to prevent the plated silver frombecoming tarnished (this is usually within about 2 hours afterelectroplating), a transparent protective coating is applied to theplated markings. This coating may consist of a single coat of waterclear organic baking lacquer or two coats of water clear air dryinglacquer. The baking lacquer is to be preferred. The lacquer is appliedonly to the front face of the panel, care being taken especially tocompletely cover the plated letters. The backs of the panels should not,of course, receive the lacquer since the plating on th exposed surfacesthereof is for electrical contact purposes.

Engraved markings formed as above described are quite smooth and silverywhite. The organic finish will not be lifted or broken at any spot, andpanels prepared in the manner set forth above will be found to withstandsalt spray tests of 100 hours or more with very satisfactory results.

Although I have described my invention in considerable detail, it willundoubtedly be apparent to thoseskilled in the art that many vvariations thereof are possible. I therefore desire that my inventionshall not be limited except insofar as is made necessary by the priorart and by the spirit of the appended claims.

I claim as my invention:

1. The method of forming engraved markings in a ferrous article whichcomprises first treating the surface of said article with a phosphate toform thereon a frosty, crystalline, even, greyblack deposit of ironphosphate, then applying thereto a finishing coating of organic materialcapable of becoming cured to a hard, firm condition in the course oftime and which, in aid condition, is insoluble in sodium cyanidesolution, then causing said finishing coat to become cured to saidcondition, then cutting said markings through said finishing coat andinto said article, then cleaning said markings with the aid of asolution of sodium cyanide, then applying a coating of cadmium thereto,subsequently electroplating a coating of silver on said cadmium coating,and finally covering aid silver coated markings with a protectivecoating of clear lacquer.

2. The invention set forth in claim 1 characterized in that saidmarkings are rendered smooth prior to cleaning thereof.

3. The invention set forth in claim 1 characterized in that saidmarkings are made in steps by first cutting through substantially onlysaid finishing coat, then cutting into said article below the surfacethereof, and finally rendering the cuts in said finishing coat and insaid article smooth prior to the cleaning thereof.

4. The method of forming engraved markings in a ferrous article whichcomprises first treating the surface of said article with a phosphate toform a coating of adherent iron phosphate thereon, then applying theretoa finishing coat of organic material capable of becoming cured to ahard, firm condition in the course of time and which, in said condition,is insoluble in sodium cyanide solution, then causing said finishingcoat to become cured to said condition, then cutting said markingsthrough said finishing coat and into said article, then cleaning saidmarkings with the aid of a solution of sodium cyanide, then applyingthereto a coating of an adherent, stable metal capable of beingelectroplated with another metal, subsequently electroplating a coatingof silver over said adherent metal coating, and finally covering saidsilver coated markings with a transparent protective coating.

CLIFFORD W. MELL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS France May 30, 1938

